This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for NOZZLE PLATE ASSEMBLY OF MICRO-INJECTING DEVICE AND METHOD FOR MANUFACTURING THE SAME earlier filed in the Russian Federation Patent Office on Nov. 3, 1998 and there duly assigned Ser. No. 98119954.
1. Field of the Invention
The present invention relates to the field of micro-injecting devices and ink-jet printheads, and particularly to a nozzle plate assembly of a micro-injecting device.
2. Description of the Related Art
Generally, a micro-injecting device refers to a device which is designed to provide printing paper, a human body, or a motor vehicle with a certain amount of liquid, for example, ink, an injection liquid, or petroleum, using the method in which a predetermined amount of electric or thermal energy is applied to the above-mentioned liquid to bring about a volumetric transformation of the liquid. Thus, a predetermined amount of such a liquid can be supplied to a specific object.
Recent developments in electrical and electronic technology have enabled rapid development of such micro-injecting devices. Thus, micro-injecting devices are being widely used in daily life. An example of micro-injecting devices in daily use is the inkjet printer.
The inkjet printer is a form of micro-injecting device which differs from conventional dot printers in the capability of performing print jobs in various colors by using cartridges. Additional advantages of inkjet printers over dot printers are lower noise and enhanced quality of printing. For by these reasons, inkjet printers are gaining immensely in popularity.
An inkjet printer is generally provided with a printhead which transforms ink which is in the liquid state to a bubble state by turning on or off an electric signal applied from an external device. Then, the ink so bubbled is expanded and expelled so as to perform a print job on a printing paper.
Examples of the construction and operation of several ink jet print heads of the conventional art are seen in the following U.S. Patents. U.S. Pat. No. 4,490,728, to Vaught et al., entitled Thermal Ink Jet Printer, describes a basic print head. U.S. Pat. No. 4,809,428, to Aden et al., entitled Thin Film Device For An Ink Jet Printhead and Process For Manufacturing Same and U.S. Pat. No. 5,140,345, to Komuro, entitled Method Of Manufacturing a Substrate For A Liquid Jet Recording Head And Substrate Manufactured By The Method, describe manufacturing methods for ink-jet printheads. U.S. Pat. No. 5,274,400, to Johnson et al., entitled Ink Path Geometry For High Temperature Operation Of Ink-Jet Printheads, describes altering the dimensions of the inkjet feed channel to provide fluidic drag. U.S. Pat. No. 5,420,627, to Keefe et al, entitled Ink Jet Printhead, shows a particular printhead design.
In general, such a conventional inkjet printhead includes a nozzle plate having a nozzle with a minute diameter for ejecting ink. During ejection, the nozzle plate serves as a jet gate for finally ejecting ink onto external printing paper, and thus functions as an extremely important component in determining printing quality. Therefore, the substances used in forming a nozzle plate, and the size and shape of the nozzle must be designed in consideration of the characteristics of the ink.
Generally, in such an inkjet printhead, an outer surface of a nozzle plate is formed smooth so as to have low roughness. Thus, the surface tension between the nozzle plate and ink increases and the contact angle between them becomes larger, thereby preventing crosstalk in which ink droplets which are bubbled and ready to be discharged flow to an adjacent nozzle.
With the outer surface of nozzle plate, the crosstalk problem can be easily rectified by decreasing the surface roughness. However, if an inner surface of nozzle plate decreases in roughness, the surface tension between the inner surface and ink increases. Thus, the contact angle between the nozzle plate and ink becomes larger. As a result, ink which is to be discharged toward a nozzle coheres at an inner surface of the nozzle plate instead of being bubbled. In this case, the cohered ink droplets cut off between an ink feed channel and ink chamber, thereby disturbing the smooth supply of ink.
If the ink supply is not smooth and thus the ink contained in an ink chamber is insufficient, when a high speed driving of a printhead is performed, a large amount of air bubbles is generated in the ink chamber. Then, the generated air bubbles prevent ink droplets from passing through the nozzle, thereby causing a problem in that the ink cannot be ejected onto printing paper. As a result, overall printing quality is significantly lowered.
To overcome such problems, U.S. Pat. No. 5,563,640, to Suzuki, entitled Droplet Ejecting Device, has disclosed a method in which an outer surface of a nozzle plate is formed of substances having poor adhesiveness to ink, for example, polysulfone, polyethersulfone, or polyimide. Meanwhile an inner surface of the nozzle plate is coated by substances having excellent adhesiveness to ink, for example, SiO2 film. Thus, different surface tensions can be maintained where the ink contacts the outer surface and the inner surface, thereby overcoming the above-described crosstalk and air bubble generation problems.
In addition, U.S. Pat. No. 5,378,504, to Bayard et al., entitled Method For Modifying Phase Change Ink Jet Printing Heads To Prevent Degradation Of Ink Contact Angles, has disclosed a method in which an additional coating substance having high durability is deposited onto an outer surface of a nozzle plate so as to prevent loss of surface tension and to maintain the state of the outer surface of the nozzle plate.
However, to form a nozzle on a nozzle plate, a complicated process using high cost equipment, for example, an excimer laser, is required. In addition, if SiO2 film is formed on an inner surface of the nozzle plate, the diameter of the nozzle becomes extremely narrow and the SiO2 film cannot be formed uniformly. In addition, because an additional coating process for depositing coating substance onto an outer surface of the nozzle plate is required, the overall process becomes extremely complicated.
To overcome this problem, an electroforming method which eliminates the additional coating process and requires a low investment cost facility can be employed. However, in this case, due to a limitation imposed by the electrolyte, the roughness of the inner surface cannot exceed 0.016 xcexcm to 0.025 xcexcm, and a desirable surface tension cannot be obtained.
It is therefore an object of the present invention to provide an improved nozzle plate for a micro-injection device.
It is a further object of the invention to provide a nozzle plate which prevents ink from cohering at the inner surface of the nozzle plate.
It is a yet further object of the invention to provide a nozzle plate which prevents crosstalk between nozzles on the outer surface of the plate.
It is a still further object of the invention to provide a nozzle plate which prevents formation of an air bubble which would cut off the supply of ink.
It is also an object of the present invention to provide an improved method for manufacturing the nozzle plate of a micro-injection device.
It is an additional object to provide a less complicated method for manufacturing the nozzle plate of a micro-injection device which produces different surface tensions on the inner and outer sides of the nozzle plate.
It is a yet additional object to provide a less expensive method for manufacturing the nozzle plate of a micro-injection device.
To accomplish the above objects of the present invention, a master plate which defines a nozzle region is dipped into an electrolyte in which NiH2/SO3/H, NiCl2, H3BO3, C12H25SO4/NaS and deionized water are mixed at a predetermined ratio. Then, a predetermined current density is sequentially applied several times, to thereby coat a nozzle plate having a plurality of nozzles onto a surface of the master plate.
Here, the surface of the master plate is polished by heat-treatment and surface-treating processes. Thus, the outer surface of the nozzle plate which contacts a surface of the master plate maintains extremely low roughness. In addition, the inner surface of the finally formed nozzle plate is formed rough by performing ionization on electrolyte formed of NiH2/SO3/H, NiCl2, H3BO3, and sodium lauryl sulfate (C12H25SO4/NaS), to thereby maintain an extremely high roughness. As a result, the surface tension of the ink which contacts an inner surface becomes smaller than that of the ink which contacts an outer surface.